Some engines operate according to a four stroke cycle comprising an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. Other engines operate according to a two stroke cycle where the intake stroke is partially shared with the compression stroke and the exhaust stroke is partially shared with the power stroke. Some engines have been developed that can be selectively operated in a two stroke cycle during some conditions and a four stroke cycle during other conditions. In this way, the engine may exhibit higher power output through selective use of the two stroke cycle while achieving increased fuel efficiency through selective use of the four stroke cycle.
The inventor herein has recognized that transitions between two and four stroke operation may be achieved in one approach by a method of operating an internal combustion engine including at least one combustion chamber having a piston disposed therein. As one example, the method includes: repeatedly opening a first intake valve of the combustion chamber once every four piston strokes; transitioning operation of the combustion chamber from a four stroke cycle to a two stroke cycle by activating a second intake valve of the combustion chamber to repeatedly open once every four piston strokes during a different intake stroke than the first intake valve; and transitioning operation of the combustion chamber from the two stroke cycle to the four stroke cycle by deactivating the second intake valve in a closed position. A similar approach may be applied to the exhaust valves of the engine as will be described herein.
In some embodiments, the above method may be performed by an internal combustion engine system for a vehicle, including: an engine body defining at least one combustion chamber having a piston disposed therein; a manifold coupled to the engine body and defining a fluid passage that communicates with the combustion chamber via a first valve and a second valve; a first cam actuator configured to open the first valve; a second cam actuator configured to open the second valve; and a control system. The first valve and the second valve may include intake valves, or the first valve and the second valve may include exhaust valves.
The control system may be configured to: operate the first cam actuator to repeatedly open the first valve once every four piston strokes and operate the second cam actuator to repeatedly open the second valve once every four piston strokes during a different stroke than the first valve to carry out combustion in the combustion chamber according to a two stroke cycle; and operate the first cam actuator to repeatedly open the first valve once every four piston strokes and operate the second cam actuator in an inactive lift state with the second valve so that the second valve is held closed to carry out combustion in the combustion chamber according to a four stroke cycle.
The intake and exhaust valves that are operated continuously during both the two and four stroke cycles may be referred to as “full time” valves, while the intake and exhaust valves that are operated during the two stroke cycle while being deactivated during the four stroke cycle may be referred to as “part time” valves. In this way, the first intake valve may continue to operate during both of the four stroke and two stroke operations, while the second intake valve may be held closed to enable the four stroke operation.